1. Field of the Invention
The present invention relates to a water repellent coating composition which is excellent in water repellence, anti-snow or ice-sticking property and weatherability, to a method of preparing such a water repellent coating composition, and to coating films and coated articles provided using such a water repellent coating composition.
The water repellent coating composition of the present invention has high water repellence, antisnow- or antiice-sticking properties, and weatherability and can be used for preventing wetting with water, adhesion of dirt or corrosion of coated surfaces. The water repellent coating composition of the present invention can be used widely in various fields including construction, civil engineering, etc.
The present invention is applicable to surface treatment of various antennae, e.g., antennae for satellite communication and satellite broadcasting, antenna domes for communication, antennae for flight control, Yagi antennae and the like in order to prevent wetting with water, adhesion of snow or ice on the surface thereof. Also, the present invention is applicable to surfaces of reflector plates for radars and radiotelescopes, iron towers, cables, transmission lines, constructions and facings thereof, such as houses, buildings, roofs or outer walls thereof, surfaces of vehicles such as electric cars, trains, automobiles, ships, airplanes, front window glasses of such vehicles, jigs for civil engineering machines, ventilation or exhaustion outlets of chimneys and stoves. The water repellent coating composition of the present invention can be provided in the form of a dispersion or contained in a spray can.
2. Description of the Related Art
Development of water repellent coating compositions having excellent water repellence, and concomittantly antisnow- or antiice-sticking property, as well as weatherability will enable realization of antennae, cables, towers, roofs and the like which are resistant to snow-sticking by coating such coating compositions thereon and such coating compositions will find their way into many uses including coating of jigs for civil engineering machines and the like. For this reason, various water repellent coating compositions are under development.
Conventional approaches to improve water repellence of an object such as glass have been to reduce as low as possible the surface energy of an object or material which needs water repellence as by coating the surface thereof with a compound containing a fluoroalkyl group, a compound containing a siloxane group, coating composition or the like or dispersing fine particles of fluoroalkyl group containing compounds in the material.
For example, use has been made of a wet plating method to compound fine particles of polytetrafluoroethylene (PTFE) with nickel metal to develop a water repellent material having water repellence in terms of contact angle of no lower than 150, which latter contact angle is deemed to be a standard of water repellence. This method cannot be applied to constructions or objects outdoors, such as buildings or houses, since the method includes plating which is inapplicable to those outdoor constructions or objects and the applicability of the method depends on the applicability of the wet plating.
Recent development in the art includes a water repellent coating composition containing powder of PTFE having a low molecular weight of 500 to 20,000 and fluorinated even to the terminals of the molecule, dispersed in an acrylic silicone resin or the like as disclosed in Japanese Patent Application Laying-open No. 122838/1994. The coating composition is reported to exhibit excellent water repellence, with a coated surface having an initial contact angle of not lower than 140xc2x0. The water repellent coating composition is expensive since it contains as water repellent powder special PTFE powder which is fluorinated to terminals of the molecule, making it difficult to provide such water repellent coating composition competitively and, hence, limiting the scope of its application. In addition, fluororesins including low molecular weight PTFE generally have low intermolecular energy so that their mechanical strength is low and coated surfaces with such resins are vulnerable to abrasion or compression and are less durable. Therefore, they can find their way in only limited applications.
Japanese Patent Application Laying-open No. 33480/1977 discloses a glass substrate with a water repellent layer comprising a porous film containing lower molecular weight PTFE in cavities thereof. In this case, the contact angle of the water repellent layer was about 110xc2x0, thus failing to give sufficient water repellence.
Also, Japanese Patent Application Laying-open No.138047/1977 proposes use of a water repellent material containing a metal oxide and a fluororesin on a surface of glass substrate. The contact angle was about 110xc2x0 and water repellence is insufficient.
The method disclosed in Japanese Patent Application Laying-open No. 138050/1977 uses a sol-gel reaction to form a subbing layer of a metal oxide on a glass substrate and coat a fluororesin thereon. The contact angle was about 110xc2x0, which is insufficient.
Further, Japanese Patent Application Laying-open No. 251060/1977 discloses a method of providing a water repellent surface on a substrate by pulverizing water repellent composite powder comprising base particles coated with low molecular weight PTFE, the base particles having mechanical strength greater than the PTFE, and making the pulverisate adhere to a surface of a substrate. The contact angle attained by the method is not smaller than 150xc2x0. However, the manufacture of the composite powder is difficult since the method involves the steps of attaching the low molecular weight PTFE having poor adhesion power to the base particles and pulverizing water repellent composite particles having excellent lubrication capability which latter step is complicated. In addition, the resulting coating composition has a poor mechanical strength since the low molecular weight PTFE film tends to be peeled off due to abrasion.
As described above, most of the conventional water repellent coating compositions have disadvantages in that they exhibit insufficient contact angles or exhibit sufficient contact angles only at high cost and manufactured with difficulty.
Further, the conventional coating compositions are also disadvantageous in that they generally produce white opaque coating films so that the color of the underlying layer or material of the coated article cannot seen as is and, hence, their application is limited considerably. In order to cope with this problem, addition of one or more pigments is mandated in order to color the coating film. The addition of such pigment(s) would often deteriorate the water repellence that the composition has inherently.
Therefore, an object of the present invention is to obviate the problems inherent to the above-described prior art and provide a water repellent coating composition having improved water repellence, anti-abrasion property, antisnow- or antiice-sticking property and weatherability economically.
Another object of the present invention is to provide a transparent coating composition.
Still another object of the present invention is to provide a method of preparing such a transparent coating composition.
Yet another object of the present invention is to provide a coating film.
Further, an object of the present invention is to provide a coated article coated with such a coating composition.
According to a first aspect of the present invention, there is provided a water repellent coating composition comprising:
fine particles having functional groups on their surface;
a coupling agent containing a functional group which is capable of reacting with the functional groups of the fine particles and a functional group; which is water repellent
a binder resin for binding the fine particles; and
a solvent for the binder.
Here, the fine particles may comprise an inorganic material.
The inorganic material may preferably be one selected from the group consisting of SiO2, SiO2 containing glass, shirasu, siliceous sand, zeolite, silicon carbide, and mixtures thereof.
Also, the fine particles may comprise an organic material.
The organic material may preferably one selected from the group consisting of polymethyl methacrylate, polyurethane resin and mixtures thereof.
The fine particles may comprise an inorganic material and an organic material in combination.
The inorganic material is selected from the group consisting of SiO2, SiO2 containing glass, shirasu, siliceous sand, zeolite, silicon carbide, and mixtures thereof, and the organic material is selected from the group consisting of polymethyl methacrylate, polyurethane resin and mixtures thereof.
The coupling agent may preferably one selected from the group consisting of silane coupling agent having a water repellent group in its molecule and a titanium coupling agent, and mixtures thereof.
The binder resin may preferably one selected from the group consisting of acrylic resin, acrylic silicone resin, acrylic urethane resin, polyester resin, epoxy resin, urethane resin, fluororesin, and mixtures thereof.
According to a second aspect of the present invention, there is provided a water repellent coating composition comprising:
fine particles having functional groups on their surface, the fine particles having a particle diameter of no greater than 1 mm;
a coupling agent containing a functional group which is capable of reacting with the functional groups of the fine particles and a functional group which is water repellent;
a binder resin for binding the fine particles; and
a solvent for the binder
wherein the fine particles differ from the binder resin in refractive index within xc2x12% based on the refractive index of the fine particles.
Here, the fine particles may exist in an amount of 10 to 90% based on the weight of the composition after evaporation of the solvent.
According to a third aspect of the present invention, there is provided a method of preparing the above-described transparent water repellent coating composition, comprising the step of treating surfaces of fine particles with a coupling agent.
Here, the fine particles may exist in an amount of 10 to 90% based on the weight of the composition after evaporation of said solvent.
According to a fourth aspect of the present invention, there is provided a method of preparing the above-described transparent water repellent coating composition, comprising the step of mixing said fine particles and said binder in an apparatus utilizing high speed turbulent flow energy.
Here, the fine particles may exist in an amount of 10 to 90% based on the weight of the composition after evaporation of said solvent.
According to a fifth aspect of the present invention, there is provided a method of preparing the above-described transparent water repellent coating composition, comprising the steps of treating surfaces of fine particles with a coupling agent and mixing said fine particles and said binder in an apparatus utilizing high speed turbulent flow energy.
Here, the fine particles may exist in an amount of 10 to 90% based on the weight of the composition after evaporation of said solvent.
According to a sixth aspect of the present invention, there is provided a coated film obtained from the above-described water repellent coating composition.
According to a seventh aspect of the present invention, there is provided a coated article comprising:
a substrate;
a coating film obtained from the above-described water repellent coating composition.
Other and further objects, features and advantages of the present invention will become more apparent from the following description of preferred embodiments with reference to the accompanying drawings.